Since the problem satisfies the Slater’s condition, the duality gap does not exist strictly [1]}. Then, by substituting \(g_3\)  into (REF ) and setting \(\partial \Gamma _1 / \partial {\bf {W}}\)  to zero, we obtain
\(\begin{aligned}{{\bf {W}}^{\rm opt}} ={\left( {\sum \limits _{b = 1}^B {{\lambda _b}{{\bf {D}}_b} + {\bf {A}}} } \right)^{ - 1}}{\bf {V}}.\end{aligned}\) 
